Process of uniting strands of a plaited polyamide article



United States Patent 3,393,111 PROCESS OF UNITING STRANDS OF A PLAITED POLYAMIDE ARTICLE Erwin Hofmann, Birkenriedstr. 5.; Fritz Giisswald, Lindenstrasse 11; and Ernst Moke, Pappelweg 9, all of Peiting, Germany; and Josef Staude, Am Hofield 3, Rottenbuch, Germany No Drawing. Filed Mar. 26, 1964, Ser. No. 355,060 Claims priority, application Germany, Oct. 4, 1963,

1 Claim. c1: 156-305) ABSTRACT OF THE DISCLOSURE The invention relates to processes for the treatment of polyamide and superpolyamide products, and specifically of fabrics, knitted goods, plaited works, cords, cordages, and injection molded goods, preferably in the form of summer shoes, sandals, sandalettes, pantolets, slippers, and watch-bands. The invention also relates to associated products.

The invention is based on the finding that it is sometimes necessary to fix the length and width of plaited goods and strips of the above-mentioned kind, and especially those which are provided with a multitude of small holes formed during manufacture, so that they undergo no subsequent change in these two directions.

Plaited articles, regardless of the raw material of which they are made, will change dimension upon being subjected to tension; i.e., they become longer and narrower.

In order to overcome this characteristic which is sometimes undesirable, it is known to provide braided bands with gussets, pipings or the like, to heat-seal such articles, or to glue the intersections of the plaited work. All these methods require special operations, or else it is necessary to use special treatment substances which change the plaited work. Further, known measures do not permit preserving or improving the smoothness of the base material. The known measures, moreover bring about the result that the plaited works attract dirt to a greater degree than they ordinarily would.

The invention is further based on the fact that it is often desirable to impart to products of the above-mentioned kind a smooth surface which can be changed from half-lustre to high-lustre.

In order to meet the above-mentioned requirements, a process is proposed according to the invention which is characterized in that formic acid is caused to act on those surface portions of the products which are to be treated.

According to one embodiment of the invention, liquid formic acid is used which preferably contains dissolved polyamide or superpolyamide. Such a solution of polyamide or superpolyamide in formic acid is preferably sprayed onto the surface portions to be treated, whereupon the formic acid is allowed to evaporate, so that the polyamide or superpolyamide which had been dissolved in the formic acid remains on the products. Said polyamide or superpolyamide forms on the product a coating organically adhering thereto.

3,393,111 Patented July 16, 1968 ICC The polyamide or superpolyamide applied in this manner combines with the polyamide or superpolyamide of the base plaited work in such a manner that a chemically uniform structure forms. In addition thereto, experience has shown that, suprisingly, the plaited work becomes smoother and, hence, more dirt repellent. More particularly, the plaited work is glued together mass-organically at all intersections of the plaited material. This mass-organic gluing at all intersections fixes the length and width in so perfect a manner that the desired result is achieved completely. The numerous small holes of the plaited work remain open, i.e., they are not clogged by the spraying process, which is of considerable importance for certain fields in which plaited works may be used.

The evaporation of the formic acid can be accelerated by subjecting the product to a heat treatment, preferably immediately after the solution has been sprayed on.

The amount of polyamide or superpolyamide required for the spraying-on process is comparatively small. Consequently, the spraying process can be repeated as often as possible after the preceding spraying has dried. One or possibly two sprayings on only one side of an article for example, a braided band, preferably on the side lo cated at the bottom during use, i.e., on the side engaging the skin are sufficient for most purposes for which the product is to be used. In special cases, for example, if the braided works are to come into contact with Water on all sides, it is advisable to spray the solution on two sides, i.e., on the lower side and on the upper side.

It is important to stress that the procedure according to the invention does not result in a bonding of the braided material nor in a gluing of the braided material, but that the braided material is chemically-organically interconnected. There is no chemical change of the braided material nor any coloring thereof.

The property of plaited works according to the invention, namely, that they have a dirt-repellent surface, i.e., that dirt practically does not adhere to them, is of special importance for many purposes for which these plaited works are used. Owing to the structure of the plaited work, previously known plaited bands or strips were rough and became dirty merely due to body perspiration. Surprisingly, this effect no longer occurs in bands or strips sprayed according to the invention. The surface of the band resting on the skin absorbs practically no perspiration; yet the skin is fully able to breathe because the holes in the plaited work are not clogged by the treatment of the invention. The plaited works according to the invention can be cleaned and freed from dust or the like in an extremely simple manner such as, for example, by being cleaned simply with water.

According to another embodiment of the invention, the formic acid is applied to various products by evaporation. It was found that hot formic acid vapor is particularly suitable, and especially vapor which is obtained by the boiling of formic acid. The desired lustrous surface is formed directly by the surface biting of the vapor treated product, which is caused by the formic acid vapor. Depending on the amount of vapor supplied and on the length of the treatment time, the lustre of the surface of the finished product will differ. Accordingly, the amount of vapor supplied and the treatment time can be varied as desired. Owing to the hot formic acid vapor, the polyamide molecules located at the surface of the product immediately melt over the entire surface which is exposed to the action of the formic acid vapor.

In addition to imparting lustre to the surface of the product treated, the method also imparts the property of making the surface highly dirt-repellent. In addition, this development of the process according to the invention firmly interconnects individual threads, bands and the like, which gives the appearance as if said threads, bands and the like, had been glued together. However, the bonding or connecting of the threads, bands and the like, in fact, takes place by the interengagement (running or flowing into each other) of the surface molecules dissolved at the points of contact of said threads, bands and the like.

Another substantial advantage of the process according to the invention consists in that the products treated according to the invention can be cut or punched, without the cut or punched fabric, knitted goods or plaited work becoming frayed. This results in a saving of material.

The evaporating process according to the invention also imparts to the products treated an extraordinarily fresh and clear appearance. Moreover, products which are vapor-treated in accordance with the invention remain soft and flexible.

The vapor-treating process according to the invention causes the loss of only a small amount of formic acid, namely of that amount which remains bound after the melting of the molecules when the drying has been completed.

In the claim which follows hereinafter, when reference is made to a product or products, this will include, but is not limited to, products of fabrics, knitted goods, plaited or braided materials, cords, cordages and injection molded articles such as summer shoes, sandals, sandalettes, pantolets, slippers, watch bands and the like.

What is claimed is:

1. A process comprising uniting the strands of a plaited polyamide or superpolyamide article by contacting said article with hot formic acid vapors to soften said strands and thereby cause the strands to be united where they contact one another.

References Cited UNITED STATES PATENTS WILLIAM D. MARTIN, Primary Examiner.

T. G. DAVIS, Assistant Examiner. 

